Folding ladders comprising multiple hinged sections are well known. Such ladders offer the conveniences of being collapsible to a compact size for ease of transportation and storage and of being extendible to a variety of lengths and configurations for use as a self supporting step ladder, a straight extension ladder or as a scaffold. Examples of folding ladders of the type of interest herein are seen in U.S. Pat. No. 3,474,881, issued Oct. 28, 1969; U.S. Pat. No. 4,815,564, issued Mar. 28, 1989; and U.S. Pat. No. 4,666,327, issued May 19, 1987.
To provide versatility in the selection of the configuration into which the ladder may be extended, the ladder sections are hinged together at their ends by pivoted joints which may be locked in any one of several selectable angular positions. The adjoining ladder sections then may be folded flat against one another for storage or transportation and may be unfolded to extend at various angles from one another and locked together for use in the desired configuration.
Examples of pivot joints or hinges of the known prior art designed for use in foldable ladders are seen in the following U.S. Pat. Nos. 3,655,012, issued Apr. 11, 1972; 3,955,240, issued May 11, 1976; 4,474,264, issued Oct. 2, 1984; 4,577,986, issued Mar. 25, 1986; 4,602,889, issued Jul. 29, 1986; 4,645,371, issued Feb. 24, 1987; 4,770,559, issued Sep. 13, 1988; 4,824,278, issued Apr. 25, 1989; and 4,805,737, issued Feb. 21, 1989.
Each of the hinges of the above-noted patents comprises two disk like members, one each of which is fixed to the end of one each of the opposed legs of two adjoining ladder sections. The disks are pivotally connected together to permit relative rotation and to secure the opposed ladder section legs together. One of the disk members includes a plurality of notches angularly spaced about the disk periphery. The other of the disk members carries a spring loaded pawl for engaging a selected one of notches of the first disk, thereby securing both disks against rotation. The second disk member also carries a lever or the equivalent for disengaging the pawl from a notch of the first disk to permit the adjoined ladder sections to be rotated to a different selected position.
Alternative means for locking the disks together are seen in the art. U.S. Pat. No. 4,666,327, issued May 19, 1987 and U.S. Pat. No. 3,811,151, issued May 24, 1974 both disclose a joint for a folding ladder in which the hinge members on the leg ends of one ladder section are formed as two disks spaced axially apart. The hinge members at the ends of the adjoining ladder section are each formed as a single disk, effectively, that fits between the spaced disks of the adjoining ladder section. The disks are journaled together for rotation about a common axis. A retractable pin is arranged to pass transversely through a hole in one of the outer disks of the hinge member at the end of a leg of one ladder section, through a selected one of several azimuthally spaced holes in the disk of the second hinge member at the end of the opposed leg of the adjoining ladder section, and finally pass into and seat in a hole in the other outer disk of the first hinge member. The holes of both disks of the first hinge member are aligned and the holes of the disks of both hinge members are spaced at the same radial distance from the axis of the hinge. By these means, the adjoining ladder sections may be locked together at a selected one of several different angular orientations.
U.S. Pat. No. 4,407,045, issued Oct. 4, 1983, discloses a hinge joint for a folding ladder with a locking mechanism similar to that of the '327 and '151 patents, except that two locking pins spaced on opposite sides of the hinge axis are provided. The pins are linked together for simultaneous retraction.
U.S. Pat. No. 4,773,503, issued Sep. 27, 1988, discloses a hinge for a folding ladder in which a disk is secured at the end of each of the opposing legs of the adjoining ladder sections. The disks of the opposed legs are journaled together in facing relationship for rotation about a common axis. The facing surfaces of each of the disks carry a toothed band so arranged that the teeth of each of the bands intermesh when the two mating disks are brought together. A camming device is mounted on one end of the axle that journals the two mating disks together to permit, in a released position, the disks to move apart axially sufficiently far to allow relative rotation between the toothed bands of the disks. In a locked position, the cam forces the disks tightly together, locking the toothed bands of the disks into engagement and preventing rotation of the hinge.
In the ladders of the above-referenced patents, the hinges joining the legs on both the right-hand and the left-hand sides of the ladder sections are identical, except that those on the left-hand side are the mirror images of those on the right-hand side. This arrangement requires that the hinges on both sides of adjoining ladder sections must be simultaneously unlocked in order to move the adjoining sections into a desired orientation. Then the hinges on both sides of the ladder sections must be simultaneously locked to secure the ladder sections in the selected orientation.
The following U.S. Patents of the known art show examples of ladders having adjustable feet for leveling the ladder:
U.S. Pat. No. 4,744,441, issued May 17, 1988, discloses a ladder having legs which terminate in a jack screw arrangement for adjusting the leg ends to different lengths to level the ladder. U.S. Pat. No. 3,447,631, issued Jun. 3, 1969, discloses a ladder having foot members slidably attached to the leg ends. An outwardly facing toothed rack bar is fixed along the length of the rear surface of each of the foot members. A U-shaped latch is pivotally secured at the front surface of the ladder leg near the end thereof so as to encircle the leg and the rack bar of the foot member with the bight of the latch overlying the teeth of the rack. The teeth of the rack are so oriented and the latch is so dimensioned that extension of a foot member relative to a leg end causes the bight of the latch to swing outward from the rack bar, disengaging the latch and permitting the foot member to slide downward along the leg. When the foot is extended to the desired length, a slight reverse movement of the foot member causes the latch to swing inward toward the rack bar and the bight of the latch to engage a tooth of the rack. The foot member is then held in place at the selected length so long as no relative movement between the foot member and the leg occurs.
The adjustable legs disclosed in U.S. Pat. No. 4,744,441 are tedious to manipulate when leveling the ladder, while the adjustable legs of U.S. Pat. No. 3,447,631 are not positively locked in place after adjustment.
Extension ladders of lightweight construction are disclosed in U.S. Pat. No. 3,009,522, issued Nov. 21, 1961; U.S. Pat. No. 4,029,172, issued Jun. 14, 1977; U.S. Pat. No. 3,502,173, issued Mar. 24, 1970 and U.S. Pat. No. 4,244,760, issued Jan. 13, 1981. In these ladders of the prior art, weight reduction is achieved principally through the substitution of resin impregnated fiber glass for wood or metal in the rails or stiles of the ladders.
U.S. Pat. No. 4,029,172 discloses a ladder in which the rails and rungs are molded as an integral piece using a foam plastic core and outer layers of impregnated fiber glass.
In the ladder of U.S. Pat. No. 3,009,532, the rails are constructed of layers of impregnated fiber glass wound on a balsa wood core. U.S. Pat. Nos. 3,502,173 and 4,244,760 disclose ladders in which the side rails are made of impregnated fiber glass, while the rungs are formed separately and are assembled to the side rails after the side rails are molded.
The ladders of light weight construction, except for that disclosed in U.S. Pat. No. 4,029,172, are fabricated in multiple steps in which the side rails and rungs are manufactured separately, then assembled and reprocessed.
Accordingly, it will be appreciated that there exists a critical need for a versatile folding ladder that is strong yet lightweight, readily portable, compact for convenient storage, has improved electrical safety, and is easy to articulate into a desired position for a variety of applications around the home or on the job, yet may be manufactured easily and economically for widespread merchandising and distribution to consumers, homeowners and do-it-yourselfers, as well as to professional mechanics, carpenters and tradesmen.